Process for the refining of naphthenic acids



Patented Oct. 4, 1938 UNITED. STATES PATENT I OFFICE jPRooEss FOR THE REFINING or NAPH- u u I i THENIC ACIDS :Hendrik Jan Donker, Emmastad, Curacao, Dutch West Indies, assignor to Shell Development Company, San Francisco, Calif., a corporation of Delaware NoDrawing. Application July 12, 1937, Serial N0. 153,295. France- August 10, 19 36 Claims; (o1. 260-514) This invention relates to a refining treatment for aqueous alkaline reacting solutions of alkali" metal naphthenates, containing impurities with which naphthenates are commonly associated.

Petroleum oils constitute the largest known source of naphthenic acids. Different petroleum oils contain different types and amounts of naphthenic acids which'are normally extractedand recovered by subjecting the oil to an extraction with dilute aqueousj solutions of alkali metal hy- I solutions most frequently employed, vary between about from 3 to the choicefbeing governed by a number of 'considerationsysuch' as nature and concentration of the naphthenic acids in the petroleum oil, nature of theoil itseljf, nature of the impurities-etc. For reasons of economy the extraction isusually carried out in a'manner to convert substantially all of the hydroxide to naphthenate, so that the resulting naphthenate solution, although being distinctly alkaline, contains but a small amount of free alkali metal hydroxide. The efliciency of the naphthenic acid extraction in generalincreases with increasing concentration of the hydroxide solution, but at the'sametime the amount of impurities which is extracted together with the naphthenic acids is increased in the same direction. Owing to the presence of impurities, the subsequently liberated recovered naphthenic acids have poor color and color stability, objectionable odor mostly due to sulfur compounds, and low acid valuesbecause of a content of neutral compounds a It is the purpose of this invention to treat the solutions of alkali metal naphthenates contain ing the usual impurities in a simple manner so that a substantial portion of undesirable components is removed. It is another purpose to produce by such treatment naphthenate solutions of sufficient purity, so that naphthenic acids liberated therefrom by acidification have improved color, color stability, odorand acid values;

I and it is a further purpose to produce in such a manner naphthenicacids'which require little, if any, further refining to meet the various standards for purity demanded by the trade.

My process consists essentially of treating an alkali metal naphthenatesolution, containing im- ,purities with which naphthenates are commonly solved in water, under conditions so that the resulting mixture is distinctly but only slightly alkaline, to effect precipitation of a small portion of the naphthenates in the form of water insoluble magnesium or calcium naphthenates. I have found-that during this precipitation undesirable naphthenates i. e., those which contribute to the objectionable properties of the naphthenic acids hereinbefore enumerated, are eliminated first, together with other undesirable components such as neutral oils, sulfur compounds, etc., while the more desirable naphthenic acids tend to remain in solution.

Instead of magnesium and calcium salts other water soluble salts of metals capableof precipitating naphthenates from their solutions or mixtures of these salts may be used, although perhaps in some instances with not/quite as good an effect. Among these metals may be-cited the remaining metals of the second group of the periodic system of elements, particularly the alkali earth metals strontium and barium; earth metals especially aluminum; the ferrous metals; etc. 7

I do not know the exact cause for this separation into components, of greater and lesser desirability, and therefore I do not wish to be bound by any theories regarding the mechanism of this fractionation. I have found that the alkalinity of the naphthenate solution after addition of the salt isof considerable importance with respect to the efiiciency of the fractionation, best results being obtained if the treated naphthenate solution is alkaline reacting but has a pH value above 9 and below 13 andpreferably below 12.4. For this reason it is desirable to adjust the alkalinity or acidity, respectively, of both the naphthenate and the salt solutions, so that after mixing a pH value within the desired range is obtained. The

control is effected most easily by first adjusting the free hydroxide content of the alkaline reacting naphthenate solution to within the optimum range in any suitable manner as by adding thereto naphthenic or mineral acids, and then using for the precipitation a substantially neutral salt solution. 7

The portion of the naphthenates in the solution which must be precipitated to effect substantial purification is quite small, usually well below 10%. In many instances precipitation of as little as and even less has resulted in a sufiicient improvement, so as to eliminate the necessity of further treatment or at least materially facilitate subsequent refining of the naphthenic acids. The percentage which should be precipitated varies with the concentration and nature of the naphthenic acids and impurities which are contained in the naphthenate solution. ,As a general rule, the larger the amount of impurities dissolved, the greater a proportion of naphthenates must be precipitated, and, it appears that naphthenates of relatively high molecular weights are in general more difficult to refine than those of lower molecular weights. Consequently a larger amount of salt to effect precipi-K tation is usually required in the treatment of naphthenate solutions produced from heavy petroleum oils as compared with naphthenate solutions produced from lighter oils.

Since so many variables must be considered, and since the degree of purity required of the naphthenic acids varies for diiferent purposes, it is impossible to establish beforehand the exact percentage of naphthenates which must be precipitated to obtain the desired improvement in the naphthenic acids. The necessary percentage, however, can be determined easily and quickly by a series of laboratory tests which are within the skill of the ordinary laboratory operator, by simply adding various amounts of a neutral aqueous solution of a magnesium or calcium salt to samples of the naphthenate solution under investigation, separating the precipitates, acidifying the clear naphthenate solutions, and comparing the liberated naphthenic acids with a standard to be met.

A very convenient source for magnesium and calcium salts is sea water which, as I have found, can be used advantageously in my process, without itself having to be purified prior to the application, except perhaps for the separation of suspended matter. For instance, I have obtained good results by adding by volume of sea water to solutions of sodium naphthenates having the requisite alkalinity, obtained by treating a straight run heavy naphtha from a naphthenic crude oil with 5 Baum sodium hydroxide solution under conditions to produce a naphthenate solution containing 12% recoverable naphthenic acids. A flocculent precipitate comprising basic magnesium and calcium naphthenates and containing a major portion of the undesirable impurities, formed and was separated. While this precipitate was quite voluminous, the basic naphthenates contained therein amounted to only about .8% of the naphthenates originally contained in the solution. The clear naphthenate solution was then acidified to liberate the naphthenic acids.

Comparing the acids so obtained against acids liberated from the naphthenate solution prior to the treatment with sea water the following results were obtained:

Naphthenic acid produce With sea Without water treatsea water ment treatment Acid value milligrams KOH per gram- 329 281 Sulphur content 0. 19% 0. 31 Color N. P. A. numbers... 3% 5 tions of 10 to 20% naphthenic acid content require as much as 100% by volume of sea water.

Iclaim as my invention:

1. In the process of purifying naphthenic acids containing impurities commonly associated therewith, the steps comprising adding to an aqueous alkaline reacting solution of an alkali metal salt of said naphthenic acids such an amount of a water soluble salt of a metal the naphthenate of which is substantially insoluble in water, as to produce a solvent phase which is slightly but distinctly alkaline reacting, and to effect precipitation of a minor portion only of the dissolved naphthenates, whereby a precipitate is formed which contains a substantial portion of said impurities, and separating the solvent phase from the precipitate phase.

2. The process of claim 1 in which the salt is added in the form of an aqueous solution.

3. The process of claim 1 in which the salt is an alkali earth metal salt.

4. The process of claim 1 in which the salt is selected from the group consisting of magnesium and calcium salts.

5. The process of claim 1 in which the precipitated naphthenic is between .5 and 10% of the naphthenate content of the solution.

6. The process of claim 1 in which the solvent phase has a pH value below 12.4.

7. In the process of purifying naphthenic acids containing impurities commonly associated therewith, the steps comprising adding to a slightly but distinctly alkaline reacting aqueous solution of an alkali metal salt of said naphthenic acids such an amount of a substantially neutral solution of a salt of a metal the naphthenate of which is substantially insoluble in water, as to produce a solvent phase and to effect precipitation of a minor portion only of the dissolved naphthenates, whereby a precipitate phase is formed which contains a substantial portion of said impurities, and separating the solvent phase from the precipitate phase.

8. The process of claim '7 in which the alkalinity of the naphthenate solution has a pH value above 9 and below 13.

9. In the process of purifying naphthenic acids containing impurities commonly associated therewith, the steps comprising adding to a slightly but distinctly alkaline reacting aqueous solution of an alkali metal salt of said naphthenic acids such an amount of sea water so as produce a solvent phase and to effect precipitation of a minor portion only of the dissolved naphthenates, whereby a precipitate phase is formed containing a substantial amount of said impurities, and separating the solvent phase from the precipitate phase.

10. In the process of purifying naphthenic acids containing impurities commonly associated therewith, the steps comprising adding to a slightly but distinctly alkaline reacting aqueous solution of an alkali metal salt of said naphthenic acids 10 to 100 volume percent of sea water, whereby a minor portion of the dissolved naphthenates are precipitated, forming a precipitate which contains a substantial portion of said impurities, and separating the precipitate from said solution.

HENDRIK JAN DON KER. 

